Interpretive Summary: Fescue is a cool season grass fed to approximately one third the grazing beef cattle in the U.S. During the summer, many cattle experience signs of disease associated with eating some varieties of fescue because the grass contains a fungus that makes a compound toxic to cattle. Two serious problems associated with eating fescue are weight loss and poor reproductive performance. This has traditionally been studied in cows. The present study tested the effect of toxic fescue on growth, hormone levels and reproductive performance in bulls. The data showed that the toxin appeared in the grass during the summer months, and decreased the traditional hormone marker, prolactin, but did not affect weight gain or reproductive character in bulls. The conclusion was that the effects of toxic fescue may be more in females than males because of the presence of testosterone in males.

Technical Abstract:
Twelve Angus bulls from 12 - 15 mo old were randomly assigned to high endophyte-infected (HE; 80%) or low endophyte-infected (LE; 10%) fescue for 16 weeks starting in April. Pasture levels of endophyte toxin (ergovaline) were determined every 4 weeks. Average daily gain, scrotal circumference, plasma testosterone and prolactin concentrations were monitored every 4 wks. At 16 wks, all bulls were castrated. Testes and epididymides were weighed and Bouin's fixed for histological examination. Seminiferous tubular diameters and epithelial surface areas were measured. Erogvaline in HE peaked in May. There was a seasonal increase in plasma prolactin which was suppressed in HE bulls. The decrease in prolactin was not correlated with any change in testis parameters. While endophyte-infected fescue has been shown to decrease weight gain and fertility in cows, the lack of effect in bulls suggests that anabolic character of testosterone may decrease the effects of toxic fescue.